Fuel control system for internal combustion engines

ABSTRACT

A fuel control system for internal combustion engines comprising a first control signal generator to produce an output voltage corresponding to an operating parameter of the engine, and a signal processing circuit including a non-linear means for deriving from the output voltage of the first control signal generator a plurality of voltages having non-linear relation with the output voltage of the first control signal generator, which are adjustable to provide for a plurality of slopes corresponding to respective subdivided portions of the fuel demand characteristic of the engine, and an amplifier-adder to amplify and add together the derived voltages so as to produce a total output voltage conforming to the engine fuel demand characteristic over the entire range of the engine-operating parameter. The pulse width of the pulse signal to energize the fuel injection valves is varied in accordance with the total output voltage from the signal processing circuit. Thus, even if the fuel demand characteristic is non-linear, it may be closely followed over the entire range of the involved engine-operating parameter in controlling the amount of fuel supplied to the engine.

United States Patent Wakamatsu et al.

[451 Sept. 19,1972

[54] FUEL CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES [72] Inventors: Hisato Wakamatsu, Kariya; Kunio Endo, Anjo, both of Japan [73] Assignee: Nippondenso Kabushiki Kaisha,

Aichi-ken, Japan [22] Filed: July 14, 1970 21 Appl. No.: 54,681

[30] Foreign Application Priority Data Aug. 9, 1969 Japan ..44/63166 [52] US. Cl ..123/32 EA, 123/119 R, 123/140 MC [51] Int. Cl ..F02m 51/06 [58] Field of Search..123/32 AE, 32 EA, 119, 139 E, 123/140 MC [56] References Cited UNITED STATES PATENTS 3,240,191 3/1966 Wallis ..123/32 EA 3,005,447 10/1961 Baumann et al ..123/32 EA 3,051,152 8/1962 Paule et al ..123/32 EA 2,867,200 l/l959 Gryder et al. ..123/32 EA Primary Examiner-Laurence M. Goodridge Attorney-Cushman, Darby & Cushman [57] ABSTRACT A fuel control system for internal combustion engines comprising a first control signal generator to produce an output voltage corresponding to an operating parameter of the engine, and a signal processing circuit including a non-linear means for deriving from the output voltage of the first control signal generator a plurality of voltages having non-linear relation with the output voltage of the first control signal generator, which are adjustable to provide for a plurality of slopes corresponding to respective subdivided portions of the fuel demand characteristic of the engine, and an amplifier-adder to amplify and add together the derived voltages so as to produce a total output voltage conforming to the engine fuel demand characteristic over the entire range of the engine-operating parameter. The pulse width of the pulse signal to energize the fuel injection valves is varied in accordance with the total output voltage from the signal processing circuit. Thus, even if the fuel demand characteristic is non-linear, it may be closely followed over the entire range of the involved engine-operating parameter in controlling the amount of fuel supplied to the engine.

5 Claims, 5 Drawing Figures F/RST .SYGNAL GENERATOR 5E G ONO S/GNAL AMP bog

GENERATOR T H/RO S/GNAL ,6,

GENERATOR FUEL CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to fuel control systems for internal combustion engines for controlling electromagnetically operated fuel injection valves in accordance with operating parameters of the engine.

2. DESCRIPTION OF THE INVENTION The fuel control system of the type pertaining to the invention usually uses an electromagnetic feedback type multi-vibrator consisting of a pair of transistors and a feedback transformer to provide for the feedback from the collector of one transistor to the base of the other transistor of the multi-vibrator. The amount of feedback, that is, the mutual inductance of the feedback transformer is varied in accordance with the negative pressure in the engine suction pipe, which is one of the engine operating parameters, thereby varying the pulse width of the pulse output of the multi-vibrator which faithfully follows the fuel demand characteristic of the engine. The pulse output is impressed on the fuel injection valve to drive it in such a manner that it is held in the operative or open position for a period equal to the pulse width, during which the fuel is injected either into the intake manifold of the engine or directly into the cylinder.

As the means to vary the mutual inductance of the multi-vibrator in accordance with the engine intake negative pressure is used a movable iron core coupled to a diaphragm converting the change in the intake negative pressure into a corresponding mechanical displacement thereof, whereby the associated motion of the movable iron core produces variation of the mutual inductance of the multi-vibrator.

The fuel demand characteristic of the engine, however, is not straightforward. By way of example, the

relation between the engine intake negative pressure and the amount of fuel to be supplied is not linear but is represented by a particular curve. Therefore, with the afore-mentioned conventional fuel control system the movable iron core associated with the multi-vibrator should have an extremely complicated configuration requiring very troublesome manufacturing steps. Besides, such a movable iron core gives rise to various problems in use such as mal-functioning due to external vibrations to deviate from the proper fuel demand characteristic, thus resulting in inferior reliability of the system.

Further, for engines having different fuel demand characteristics the pitch of the windings of the feedback transformers, dimensions of the diaphragm to convert engine intake negative pressure into mechanical displacement and the configulation of the movable iron core coupled to the diaphragm should be basically changed. In other words, the above conventional system totally lacks in compatibility with engines of different ratings.

SUMMARY OF THE INVENTION An object of the invention is to provide a fuel control system for internal combustion engines comprising a first signal generator to produce a voltage output corresponding to an operating parameter of the engine, and a signal processing circuit to modify the output of the first signal generator to introduce a non-linear character approximating the fuel demand characteristic of the engine by deriving from the output of the first signal generator a plurality of modified output components through respective circuits each providing an output pattern peculiar to a corresponding one of a plurality of subdivided'parts of the engine fuel demand characteristic over the entire range of the involved engine-operating parameter and amplifying and adding together the respective derived voltage components through an amplifying means, whereby the pulse width of the pulse signal impressed on the fuel injection valve is varied in accordance with the voltage output of the signal processing circuit to meet the entire engine fuel demand characteristic.

According to the invention, an excellent advantage is featured in that the pulse width of the pulse signal impressed on the fuel injection valve can be continually and exactly varied in accordance with a non-linear engine fuel demand characteristic over the entire range of the engine-operating parameter, thus enabling exact control over the amount of fuel supplied to the engine in accordance with the fuel demand characteristic of the engine with an extremely simple circuit construction. Another advantage featured by the invention is that it is possible to adopt the system according to the invention to various engines with different fuel demand characteristics by an extremely simple measure of merely varying the non-linear character of the nonlinear means producing a plurality of modified output components and the gains for the respective modified output components to suit a given engine fuel demand characteristic so as to exactly and faithfully control the amount of fuel injected in accordance with the fuel demand character of a particular engine. This means that the fuel control system according to the invention has an extremely simple requisite of merely varying the non-linear character of the non-linear circuit means and the gains involved in the aforesaid signal processing circuit for the compatibility with engines of different ratings.

Another object of the invention is to provide a fuel control system for internal combustion engines, which further comprises other two signal generators, in addition to the first signal generator, to produce a voltage output corresponding to another operating parameter of the engine for addition to the signal processing circuit.

According to the second aspect of the invention, the pulse width of the pulse signal impressed on the fuel injection valve, that is, the amount of the fuel injected during the period of the pulse width, may be increased by an amount corresponding to the output voltages component for the output of the two signal generator. This is an excellent advantage in that a desired engine output torque may be produced when the engine is under a low temperature condition and/or accelerating condition, at which time the fuel supply should be increased.

BRIEF DESCRIPTION OF THE INVENTION FIG. 1 is a block diagram of a preferred embodiment of the fuel control system for internal combustion engines according to the invention.

FIG. 2 is a schematic circuit diagram, partly in block form, showing the principal part of the system of FIG.

FIGS. 3 to are graphs illustrating the operation of the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention will now be described in conjunction with a preferred embodiment thereof with reference to the drawings.

Referring to FIG. 1, numeral 1 designates a first signal generator. In this embodiment it is a negative pressure signal generator to produce output voltage proportional to the negative pressure in, for instance, a four-cylinder engine intake manifold (Not shown). Numeral 2 designates a second signal generator to produce output voltage in inverse proportion to the engine temperature. It is actually a fuel increase signal generator to generate a fuel increase signal when the engine is in a low temperature condition, for instance when the engine temperature is below 40C, so as to ensure smooth operation of the engine at low temperatures. Numeral 3 designates third signal generator. It is also a fuel increase signal generator to generate a fuel increase signal on the basis of the action of a switch, which is closed when the engine intake negative pressure reaches a predetermined value, so as to increase fuel supply particularly under the high-load and accelerating conditions of the engine for obtaining a desired engine output torque. The voltage outputs of the first signal generator 1 the second signal generator 2 and the third signal generator 3 are fed to a signal processing section 4, which produces output voltage e containing voltage components with respective gains to the corresponding inputs (to be described hereinafter in detail) Numeral 5 designates a switch constituting an ignition start signal generator. It is operated (opened an closed) synchronously with the fuel injection timing for the first cylinder of the four-cylinder engine, for example. In synchronism with the closure of the switch 5, a saw-tooth wave generator 6 generates a saw-tooth wave signal having a constant rise time. The fuel injection cycle time for the first cylinder is indicated at T. The saw-tooth wave voltage output of the saw-tooth wave generator 6 and the voltage output appearing at output terminal 4a of the signal processing section 4 are fed to a pulse signal generator 7, which produces a pulse signal with pulse width W corresponding to the output voltage at the output terminal 4a. The pulse signal from the pulse generator 7 is fed to a fuel injection valve drive 8, which energizes an electromagnetic solenoid (not shown) of a fuel injection valve 9 in response to the received pulse signal to drive the fuel injection valve 9 such that it is held in the operative or open position for a time interval equal to the pulse width W in each fuel injection cycle. The fuel injection valve 9 is provided in the first cylinder.

The switch 5, the sawtooth wave generator 6, the pulse signal generator 7, the fuel injection valve drive 8 and the fuel injection valve 9 constitute a fuel injection subsystem for the first cylinder. Similar subsystems are also provided to the remaining second to fourth cylinders respectively, and the output voltages appearing at output terminals 4b, 4c and 4d are similarly added to the respective pulse signal generators.

The circuit construction of the signal processing section 4 is shown in detail in FIG. 2. Referring to FIG. 2, numeral 10 designates an amplifier, numeral 11 a feedback resistor (with resistance R) to provide for the negative feedback from the output side to the input side of the amplifier l0, numerals 12 to 14 gain correction variable resistors connected to a common point at one end and to the earth at the other end, numeral 15 a gain adjustment resistor (with resistance R!) connected between a movable tap 12a of the variable resistor l2 and the input terminal of the amplifier 10, numeral 16 a gain correction constant-voltage diode connected between the movable tap 12a and the earth, numeral 17 a gain adjustment resistor with resistance R2 connected between a movable tap 13a of the variable resistor 13 and the input terminal of the amplifier 10, numeral 19 a gain correction constant-voltage diode connected between a movable tap 14a of the variable resistor 14 and a gain adjustment resistor (with resistance R3), which is in turn connected to the input terminal of the amplifier l0, numeral 20 a potential adjustment variable resistor with its movable tap 20a connected through a gain adjustment resistor 21 (with resistance R4) to the input terminal of the amplifier l0, numeral 22 a gain adjustment resistor (with resistance R5) connected between the output terminal of the second signal generator 2 and the input terminal of the amplifier l0, and numeral 23 a gain adjustment resistor (with resistance R6) connected between the output ter-. minal of the third signal generator 3 and the input terminal of the amplifier 10. The ratio of the components of the voltage output from the amplifier 10 to the respective voltage outputs from the first to third signal generators 1 to 3 depends upon the ratio between the resistance R of the feedback resistor to each of the resistances R 1, R2, R3, R4, R5 and R6 of the respective gain adjustment resistors l5, l7, 19, 21, 22 and 23.

To describe the operation of the fuel control system of the above construction according to the invention, it is assumed that the fuel demand characteristic of the engine is given by a curve A-B as shown in FIG. 3, where the ordinate represents the fuel amount Q to be injected in one fuel injection cycle and the abscissa represents the engine intake negative pressure P (mm Hg). The curve A-B represents the normal fuel demand characteristic without requiring additional increase of fuel supplied. If the engine intake pressure P builds up beyond point P with increase in the engine load, the fuel demand characteristic given by curve A-B is replaced with a fuel demand characteristic given by curve C-D, according to which the amount of fuel to be injected is increased by an amount Q with respect to that according to the characteristic of curve A-B for the same intake negative pressure. When the absolute value of the intake negative pressure becomes lower than P the characteristic of curve A-B is recovered. Meanwhile, if the engine temperature is below, for instance, 40C, the fuel supply is increased by an additional amount 0 over the entire range of the engine intake negative pressure, thus replacing the fuel demand characteristics given by curves A-8 and C-D with shifted fuel demand characteristics as represented by dashed curves A'-B and C'-D'. When the engine temperature exceeds, for instance, 40C the characteristics of curves A-B and OD become available again.

The fuel amount Q to be injected is proportional to the period, during which the fuel injection valve is held in the operative or open position, and which depends upon the output voltage e produced by the signal processing section 4. Thus, it is desirable that the output characteristics for the output voltage e produced by the signal processing section 4 are similar to the fuel demand characteristics of FIG. 3 for the fuel amount 0 to be injected, as shown in FIG. 4. However, a voltage output characteristic identical with the curve A-B cannot be obtained over the entire range of the intake negative pressure in what ever way, so long as the output voltage produced by the negative pressure signal generator 1 is applied to the amplifier only through the path of the gain correction variable resistor 13 and the gain adjustment resistor 17. Accordingly, the output of the negative pressure signal generator 1 is adopted to be applied to the amplifier 10 through a plurality of paths, namely three paths in this embodiment, so as to have three simultaneous inputs to the amplifier 10 to be amplified and added together therein. This enables approximating the curve A-B by dividing it into suitable parts, for instance three parts A-F, F-E and E- B, for appropriately adjusting the relevant circuit parameters.

To describe in further detail, the circuit of the gain correction variable resistor 13 and the gain adjustment resistor 17 provide a first voltage e on the line between said variable resistor 13 and said gain adjustment resistor 17, whose slope with respect to the engine negative pressure is adjustable to approximate the segment E-B, the circuit of the gain correction variable resistor 12, the gain correction constant-voltage diode l6 and the gain adjustment resistor 15 provide a second voltage e on the line between said diode 16 and said gain adjustment resistor 15, whose slope is adjustable to approximate the segment F-E, and the circuit of the gain correction variable resistor 14, the gain correction constant-voltage diode 18 and the gain adjustment resistor 19 provide a third voltage e on the line between said diode 18 and said adjustment resistor 19, whose slope is adjustable to approximate the segment A-F. The relationship between the input voltage e to the amplifier 10 and the engine intake negative pressure P (mm Hg) is shown in FIG. 5. In the Figure, plot H-I represents the first voltage e',, plot G-F-K represents the second voltage e' and plot G-L represents the third voltage e' Point E (corresponding to point E in FIG. 4) is determined by the breakdown voltage of the gain correction constant-voltage diode l8 and the resistance of the gain correction variable resistor 14, and point F (corresponding to point F in FIG. 4) is determined by the breakdown voltage of the gain correction constant-voltage diode 16 and the resistance of the gain correction variable resistor 12. The first, second and third input voltages e,, e' and e';; are respectively amplified by the ratios of RlR R/R and R/R and then accumulated with a resultant output e through the amplifier 10. It will be appreciated that by suitably setting the values of R R and R the slope of the output voltage e, which appears from the signal processing section 4, with respect to the engine intake negative pressure may be made to approximate the curve A-B over the entire pressure range. As the pulse width of the pulse output from the pulse signal generator 7 varies in proportion to,the output voltage e from the amplifier 10, the amount of fuel supply to the engine can faithfully follow the fuel demand characteristic represented by the curve A-B in FIG. 3. In FIG. 5, plot M-N represents a potential correction voltage (corresponding to a fourth voltage) 'given by the potential adjustment resistor 20, plot O-R an output voltage (corresponding to a fifth voltage) from the temperature detection fuel increase signal generator 2, and plot S-T an output voltage (corresponding to a sixth voltage) from the pressure detection fuel increase signal generator 3. The potential correction voltage given by the potential adjustment resistor 20, which corresponds to the fourth input voltage e, with a gain determined by R/R.,, is also fed together with the first, second and third input voltages e' e and e';, to the amplifier l0, and it contributes a constant output voltage component to the output voltage of the amplifier 10 over the entire pressure range, as indicated at e in FIG. 4.

When the engine temperature is below a predetermined value, for instance 40C, the temperature detection fuel increase signal generator 2 provides an output voltage, which gives rise to the fifth input voltage e' determined by R/R for impression together with the first to fourth input voltages e,, e e';, and e, on the amplifier 10. As a result, the curve A-B for the fuel demand characteristic is shifted to establish a new curve A'-B' over the entire range of the engine intake negative pressure. Thus, the output voltage e for the same negative pressure is increased by an amount e accounting for the fifth input voltage e' This means an increase of he pulse width of the output pulse produced by the pulse signal generator 7 by an amount corresponding to the additional component e of the output voltage e from the amplifier 10. In this manner, the engine may be operated smoothly when the engine temperature is low, at which time an increased amount of fuel should be supplied to the engine.

When the engine intake pressure P exceeds the value P in FIG. 3, the pressure detection fuel increase signal generator 3 produces an output voltage, which gives rise to the sixth input voltage e' determined by R/R for impression together with the first to fourth input voltages e',, e' e' and e, on the amplifier 10. As a result, the curves A-F and GD for the fuel demand characteristics over a pressure range higher than P are replaced with respective new curves A'-F' and C'-D'. Thus, the output voltage e is increased by an amount e, accounting for the sixth input voltage e This also means an increase of the pulse width of the output pulse produced by the pulse signal generator by an amount corresponding to the additional component e of the output voltage from the amplifier 10. In this manner, fuel supply may be increased to increase the engine output torque when the engine load is high and/or acceleration is applied to the engine.

The output characteristic of the signal processing section 4 may be patterned after various fuel demand characteristics of different engines by appropriately varying the resistance of the gain correction variable resistors l2, l3 and 14, the breakdown voltage of the constant-voltage diodes l6 and 18, the resistance of the gain adjustment resistors 15, 17 and 19 and the resistance of the feedback resistor 11 such that the output voltage e of the amplifier 10 conforms to a given fuel demand characteristic. In some cases, the number of parallel current paths between the first signal generator 1 and the amplifier may be increased or decreased to provide for a corresponding number of slopes approximating to the respective part of a given characteristic curve.

Although in the foregoing embodiment the first signal generator 1 is described as a negative pressure signal generator to generate electric signal corresponding to the engine intake suction pipe negative pressure, i.e., an electric signal corresponding to an engineoperating parameter, it may replaced with a signal generator that produces an electric signal corresponding to a different engine-operating parameter such as engine speed, throttle opening and pressure in other parts of the engine. Also, the second and third signal generators are not limited to the temperature detection fuel increase signal generator 2 and the pressure detection fuel increase signal generator 3 as in the preceding embodiment, but other signal generators adopted to detect the conditions for increasing the fuel supply from the engine speed and throttle opening may be used as well. Further, the non-linear element for deriving from the output voltage of first control signal generator a plurality of voltages having non-linear relation with said voltages is not limited to the constantvoltage diodes 16 and 18, but other types of diodes, transistors and combinations of these elements may also be used. Furthermore, the invention is not limited to the four-cylinder engine as in the above embodiment, but it may also be applied to the single-cylinder engine, two-cylinder engine, three-cylinder engine and engines having five or more cylinders.

We claim:

1. A fuel injector for an internal combustion engine having a solenoid valve mounted in said engine so as to inject fuel when in an open position and responsive to an electrical signal for shifting into said open position comprising:

means for detecting an engine operating parameter and producing an electrical signal varying as a function of said parameter,

means connected to said detecting and producing means for receiving said electrical signal and producing a first linear and a second non-linear signal which each vary as a function of engine fuel demand characteristics, including resistive means connected to said detecting and producing means and a zener diode connected to said resistive means for shifting from a first to a second resistive condition to vary the ratio between the amplitude of the second signal and the received signal when said received signal reaches a predetermined amplitude,

means connected to said receiving and producing means for adding said first and second signals to produce a control signal, and

pulse generating means connected to said adding means for receiving said control signal and producing successive valve shifting electrical signals each having a duration which varies with said control signal so that said valve is in said open position successively for a duration which is a function of said engine operating parameter and said engine fuel dema nd characteristics. 2. An injector as in claim 1 further including means for detecting a second engine operating parameter and producing a second electrical signal varying as a function of said second parameter, means connecting said second engine parameter detecting and producing means to said adding means so that said adding means adds said first and second non-linear signals and said second signal to produce said control signal.

3. An injector as in claim 2 further including means for detecting a third engine operating parameter and producing a third electrical signal varying as a function of said third parameter, means connecting said third engine parameter detecting and producing means to said adding means so that said adding means adds said first and second non-linear signals, said second signal and said third signal to produce said control signalv 4. An injector as in claim 3 wherein said first operating parameter is negative pressure, said second operating parameter is temperature and said third operating parameter is high acceleration.

5. An injector as in claim 1 wherein said adding means includes an operational amplifier. 

1. A fuel injector for an internal combustion engine having a solenoid valve mounted in said engine so as to inject fuel when in an open position and responsive to an electrical signal for shifting into said open position comprising: means for detecting an engine operating parameter and producing an electrical signal varying as a function of said parameter, means connected to said detecting and producing means for receiving said electrical signal and producing a first linear and a second non-linear signal which each vary as a function of engine fuel demand characteristics, including resistive means connected to said detecting and producing means and a zener diode connected to said resistive means for shifting from a first to a second resistive condition to vary the ratio between the amplitude of the second signal and the received signal when said received signal reaches a predetermined amplitude, means connected to said receiving and producing means for adding said first and second signals to produce a control signal, and pulse generating means connected to said adding means for receiving said control signal and producing successive valve shifting electrical signals each having a duration which varies with said control signal so that said valve is in said open position successively for a duration which is a function of said engine operating parameter and said engine fuel demand characteristics.
 2. An injector as in claim 1 further including means for detecting a second engine operating parameter and producing a second electrical signal varying as a function of said second parameter, means connecting said second engine parameter detecting and producing means to said adding means so that said adding means adds said first and second non-linear signals and said second signal to produce said control signal.
 3. An injector as in claim 2 further including means for detecting a third engine operating parameter and producing a third electrical signal varying as a function of said third parameter, means connecting said third engine parameter detecting and producing means to said adding means so that said adding means adds said first and second non-linear signals, said second signal and said third signal to produce said control signal.
 4. An injector as in claim 3 wherein said first operating parameter is negative pressure, said second operating parameter is temperature and said third operating parameter is high acceleration.
 5. An injector as in claim 1 wherein said adding means includes an operational amplifier. 